Planographic printing plate



Julv 26, 1955 c, L, JEWETT ET AL 2,714,066

PLANOGRAPHIC PRINTING PLATE Original Filed Aug. 16, 1954 LIGHT-5EN5ITIVE DIAZO RESIN SILICATE TREATMENT ALUMINUM SHEET 10 /j-* ALUMINUM SHEET SILICATE TREATMENT COATING of IMAGE DEVELOPER LIGHTREACTED DIAZO RESIN SILICATE TREATMENT ALUMINUM SHEET INVENTORS CLIFFORD LJEWETT JOHN M. CASE w mmf ATTORNE 5 LIGI-IT-REACTED DIAZO RESIN United States Patent i PLANOGRAPHEC PRINTING PLATE Cliliord L. .lewett, Minneapolis, and John M. Case,

Mounds View Township, Ramsey County, Minn, assignors to Minnesota Mining & Manufacturing Company, St. Paul, Minn., a corporation of Delaware Original application August 16, 1954, Serial No. 450,149. Divided and this application July 5, 1955, Serial No. 519,900

5 Claims. or. as-s This invention relates to planographic printing plates. it particularly concerns plates of a type which may be used on well known commercial forms of lithographic presses. This application is a continuationdn-part of our copending application Serial No. 199,5 66, filed December 6, 1950, and is a division of our application Serial No. 1:

450,149, filed August 16, 1954.

Our invention is especially concerned with a plate formed from a thin metal sheet having at least one surface thereof reated to provide a tightly bonded, thin, preferably inorganic, hydrophilic surface formed from a solution of an alkali metal silicate, silicic acid, or other treating agent which will form a permanently hydrophillc scum-preventing and tone-reducing film overlying and in firmly-bonded contact with the surface of the plate, and having a coatin of light-sensitive organic material such as a light-sensitive diazo resin or other light-sensitive organic nitrogen-containing material over the exposed hydrophilic treated surface, i. e. over the exposed surface of the scum-preventing and tonereducing film or treatment. is preferably a water-soluble, rapidly light-insolubilized organic compound, especially a diazo type of light-sensitive material, as more fully described below.

Lithographic plates of one type and another have been known for a great many years; for example, see Stevens, U. S. Patent No. 556,380, granted March 17, 1896, which is one of the early patents connected generally with this subject. Zahn, U. S. Patent No. 2,100,063, granted November 23, 1937; and Toland et al., U. S. Patent No. 2,373,357, granted April 10, 1945, are examples from a large number of other patents which describe various forms of lithographic plates, and which have been granted since the aforesaid Stevens patent.

Prior to the present invention the lithographic plates employed in commerce and industry have consisted mainly of grained zinc plates, commonly produced by people who are in the business of graining plates. These grained plates are customarily supplied to a large number of shops throughout the country that make finished plates for the printer and lithographer. These shops coat the grained zinc plates with a suitable composition, normally colloidal and most usually an albumin, ammonium bichromate solution and then, following drying, promptly expose the sensitized plate, through a suitable stencil or negative, to secure the desired image, then apply a developing ink (by swabbiug) to the entire surface of the plate, then wash the entire plate with water to wash oil the unexposed colloidal and water-soluble materials and developing ink adhering thereto (which develops the image, whereupon the plate maker can see whether he has a good plate and the light-reacted albumin-bichromate layer is thus protected from water, so that it remains inkreceptive), then they apply a guru arabic solution to the printing surface of the plate, and then supply the finished plate to the printer or lithographer, for use on his presses.

One of the major disadvantages of the type of plate just described is that it must be coated with a light-sensitreatment, .I

The light-sensitive material i atented July 26, 1955 tive coating just shortly prior to exposure (through a negative or stencil) because, upon storage, the ammonium bichromate and albumin will react slowly, even in the dark at room temperatures, insolubilizing the colloid coating and rendering the plate unfit for use. Nonetheless, grained zinc plates, se sitizcd and exposed as just described, had (prior to this invention) long been the standar type of lithographic plate employed in commerce and industry when good reproduction was desired. Much of the printed matter or designs, produced by lithographic processes, had been (prior to this invention) and presently much of it still is, made with the type of zinc plate above described. While a rather large number of direct image paper plates has recently been used, they are employed only where a relatively few reproductions are needed and where high quality reproductions are not important.

One of the purposes of this invention is to provide planographic plates which are presensitized, i. e. are ready for an exposure through a negative or stencil without further treatment. These plates can be stored for considerable periods of time, i. e. weeks or months, and still be used, merely upon exposure to light through a negative or stencil, followed by washing off the unexposed light-sensitive material.

We are aware that others have previously attempted to make presensitized lithographic plates, and have succeeded in making plates which have found some commercial acceptance. However, these prior presensitized lithographic plates, which have made a limited appearance on the market, have been made with paper, plastic, or like stretchable backings to which a colloidal material had been applied. The paper hacked and plastic backed presensitized lithographic plates are the only types of presensitized plates which made their appearance on the market prior to our invention. Both of these presensitized plates have had a very limited usefulness and acceptance, for a number of reasons, especially their short press life and their lack of dimensional stability, that is, their tendency to stretch and distort the desired images.

Where attempts have been made to employ a metal plate and attach an organic colloid material thereto, these elforts have failed to meet with commercial success for any or all of a number of reasons, including (a) lack of dimensional stability of the organic colloid coating, and (b) susceptibility of the coating to stretching and abrasion, which meant that the image desired was easily damaged and only a limited number of impressions could be run off from a single plate, as Well as other reasons. In this general connection, attention is directed generally to the following: Zahn, U. S. Patent No. 2,100,063, granted November 23, 1937; the publication Light Sensitive Reproduction Materials, prepared by Field Information Agency, Technical United States Group Control Council for Germany, bearing a date of November 24, 1945, e. g. page 5 thereof; a German application of a Kalle & Co., A. G., which bore a date of August 31, 1942, and was apparently subsequently published, and makes reference in the body thereof to German Patent No. 581,697, which is equivalent to Schmidt and Zahn U. S. Patent No. 2,063,631, granted December 8, 1936; and Stevens, U. S. Patent No. 556,380, granted March 17, 1896.

However, insofar as we are aware, no one has ever previously produced any commercially acceptable presensitized metal-backed planographic plate; and no one has ever previously produced any presensitized planographic plate of any construction which will compete with grained zinc plates of the prior art, as above described, Where long press life and quality reproductions are important. Our plate, on the other hand, is a presensitized metal plate, and yet will produce work with a sharpness of dots and lines, and other details, considerably beyond what can be produced with the conventional commercial albumin-coated grained zinc plates of the prior art.

Light-sensitive diazo resins and other like light-sensitive organic materials are notably sensitive to metals. For example, Kalle British Patent No. 699,413, published November 4, 1953, at page 1, points out that if water soluble diazo compounds, or like light-sensitive substances, are coated on metal supports, a plate which can be stored in the unexposed state, i. e. a presensitized plate, cannot be made, owing to the decomposition of the light-sensitive substance caused by the metal. Others concerned with metal plates have coated them with a substantial layer of cellulose acetate, or other material, and then hydrolyzed the surface of the acetate and coated the diazo resin or equivalent thereover. No one, insofar as we are aware, ever visualized that aluminum or other metal plates could be used to receive a coating of a lightsensitive diazo resin, or the like, by the simple expedient of first briefly treating the metal surface with an aqueousalkali' metal silicate, silicic acid, or equivalent, which will give the metal a permanently hydrophilic surface, e. g. a scum-preventing surface film, and will not measurably increase the thickness of the metal plate. Furthermore, a plate madeas just indicated has outstanding quality and performance characteristics, not possessedbyany prior plate, and this was also entirely unappreciated heretofore, to the best of our knowledge and belief.

While Kalle French Patent No. 904,255, of February 19, 1945, suggests certain treatments for aluminum in the making of lithographic plates, such suggestions never proved practical or commercially useful, for various reasons: see Affidavit executed August 6, 1954, of record in our parent application Serial No. 199,566.

, It is an object of our invention to provide a presenti- .tized lithographic plate which avoids the various defects of prior art presentizide plates, as above illustrated. It

-'is also an object of our invention to provide a presensiitized plate which can replace the prior art method, cumbersorhe under many circumstances, of securing grained 'Zinc plates and then subsequently coating the same with V a light-sensitive colloidal coating. A further object is to provide a presensitized plate which preferably is free of surface roughness or grain, and from which sharp lined impressions can be produced and from which printing of high resolution, that is, extreme clarity of detail of the printed matter, can be obtained. A further object is to provide a presensitized lithographic plate of high dimensional stability which will be suitable for applications where accurate registration is required such, for example, as in multicolor work, where the same sheet is successively printed from different lithographic plates. Another object is to provide, for the first time, a commercially acceptable presensitized lithographic plate. Other objects and advantages will appear from the description taken as a whole.

To illustrate a preferred form of our invention, reference is made to the appended drawing in which:

Fig. 1 shows an aluminum sheet 10, in broken-away view, showing a scum-preventing film or thin silicate treatment 11 tightly and. chemically bonded to one surface of the aluminum sheet 10;

Fig. '2-is like Fig. 1 but additionally has a thin coating 12 of a water-soluble light sensitive diazo resin coated over or absorbed by the said silicate coating;

Fig. 3 is like Fig. 2 except the plate of Fig. 2 has .been exposed to ultraviolet light through a photographic negative and then washed with water or standard gum arabic fountain solution, leaving the hydrophobic and organophilic diazo image 12a; and

Fig. 4 is like Fig. 3 except that the exposed plate of Fig. 3 has its image surface wiped with an image developer, leaving an extremely thin coating of image developer 13.

All'dimensions in the drawing are greatly'exaggerated for clarity of illustration. The aluminum sheet 10, though being a foil having a thickness of only about .005 to .012 inch, is shown in broken-away view, in respect to its thickness as well as its length, to illustrate the fact that the silicate treatment 11 is really very thin compared with the aluminum foil 10. The silicate treatment is probably little more than -a monomolecular layer.

The coating of diazo light-sensitive resin 12 is shown in the drawing as also being a very thin coating, but it is not the intention in the drawing to illustrate whether the light-sensitive diazo resin coating is equal to, greater than, or less than the thickness of the silicate treatment. Actually, the diazo coating is apparently absorbed to some extent in the surface of the thin silicate treatment.

A salient embodiment of our invention consists in providing a thin treatment or film, probably often substantially of monomolecular thickness, of a hydrophilic inorganic material (e. g. formed from treatment with an alkali metal silicate solution) on a surface of a given metal plate, for example, an aluminum plate. The aluminum plate may be from .005 to .012 inch in thickness, although this obviously depends upon the type of press on which the plate is to be employed and other factors, and these dimensions may be greatly varied as circumstances permit. Over the exposed silicate treated or like hydrophilic and scum-preventing surface, we apply a thin coating of preferably a water-soluble lightsensitive diazo resin. This product, following drying, may be packaged in any convenient ligh -proof container, and shipped to the customer in a distant city or State. When the customer desires to use the plate, which may be many weeks, or even months, after the plate was manufactured and shipped to him, he will remove the plate from its package under subdued light, place it in contact with a negative or stencil, then expose it to a source of ultraviolet light for a short period of time, e. g. from 1 to 5 minutes, depending upon the intensity of the ultraviolet light, and then wash the surface of the plate with Water, whereupon the unexposed diazo material (that shielded by the stencil or negative), which remains water-soluble, is cleanly washed off, leaving the hydrophilic silicate treated surface exposed in those areas. The portion of the diazo coating which was exposed to the ultraviolet light was thereby insolubilized and rendered hydrophobic and organophilic (that is, water-repellent and ink-receptive), expelling nitrogen from the molecule in the process. During such exposure and insolubilization of the diazo light-sensitive material it becomes very strongly bonded to the surface of the scumpreventing film, which is usually an inorganic material such as a silicate. This plate is then ready to be placed on a lithographic press, without further treatment, and used in printing or reproducing the desired writings or images. However, before placing it on the lithographic press, it is advantageous to treat the printing surface of the plate with what, for want of a better term, might be referred to as an image developer. The image developer may take various forms. One example is a pigmented resin emulsion which will adhere to the inkreceptive areas but will not adhere to the hydrophilic areas of the plate. A printers developing ink can also be 'used'as an image developer. An example of an image developer, which we have found to be particularly useful, is described in a copending application of Myron W.

4- l-iall, entitled Planographic Printing-Plate image De veloper, Serial No. 239,841, filed August 1, 1951.

The image developer is of this practical importance: prior to the application of the image developer, the image is not visible. If a plate in that form is presented to the lithographer or printer, he cannot be sure whether he is putting the plate on the press correctly or whether he has it backwards. Additionally, in the absence of the visible image, the ressman would not know whether he had an exposed plate, unless this were denoted by some coding system or such like. In addition to making the image visible, so the pressman can see it, a good image developer also (a) helps the plate to ink up more readily when placed on the press, and (b) strengthens the image so that more copies can be run from a single plate, while still getting clear reproductions.

In order better to illustrate our novel planographic plate, we will now describe in detail a specific method of making one specific form of our plate.

Example Aluminum foil or sheet material of about .005 inch in thickness is first made ready for treatment with a silicate. Since greasy lubricants are commonly used in aluminum mills during the rolling operation, it is first desirable to treat the aluminum foil or sheet so as to remove any greasy film, so that the surface exposed will be an aluminum surface. One method which we have found to be advantageous in cleaning the aluminum surface is to immerse the same in a solution of trisodium phosphate for a sufiicient time only to clean the aluminum, e. g. for a period of 5 minutes. The temperature of the solution may be controlled at approximately 160 F. Higher temperatures may be used with a corresponding reduction in the time of treatment, and lower temperatures may be used with a corresponding increase in the time of treatment; and other solution concentrations may be used, if desired. The cleaning or degreasing of the aluminum foil or sheet material in the manner outlined above will often develop a black scum or residue on the surface of the aluminum (which probably consists primarily of oxides and hydroxides of alloyed metals) which must be either thoroughly wiped or washed away mechanically or dissolved in an acid solution such, for example, as concentrated nitric acid. If there is no scum, then there is nothing to clean away;

but if there is a black scum, we have found that nitric acid of about concentration, employed at room temperatures, will clean the scum off of the surfaces of the aluminum foil or sheet material and leave it in good condition for the subsequent steps of our plate making operation. (Aluminum is passive to 70% nitric acid.) After treatment with the acid solution, the aluminum foil or sheet material is thoroughly rinsed with water to remove any residual acid.

The cleaned surface of the aluminum is then treated with a solution of an alkali metal silicate, calcium silicate, silicic acid, colloidal hydrated silica or polymerized silicic acid (such as Du Ponts Ludox), or equivalent,

for the purpose of rendering the sheet permanently hydrophilic. We have found it advantageous to use a relatively dilute solution of a sodium silicate, potassium silicate or calcium silicate, but preferably sodium or potassium silicate, and of these sodium silicate is less expensive and fully as satisfactory. A suitable type of sodium silicate can be chosen from those commercially available having a silica to soda ratio within the range from 3.2 to 1 to 1.8 to 1; and a particularly suitable one is Star Brand, of Philadelphia Quartz Company, having a silica to soda ratio of 2.50 to l. The concentration of the sodium silicate in the solution may advantageously be about 2 to 5%, e. g. 2%, although weaker or stronger solutions can be employed.

Calcium silicate and silicic acid are relatively insoluble in water (less than one percent) and are commonly described as being insoluble in water. Insolubility, however, it is not total, a saturated solution of each containing probably in excess of .01 of one percent of the respective chemicals in solution. Regardless of the concentration achieved, saturated solutions of calcium silicate and silicic acid are sufficient usefully to treat an aluminum sheet prior to applying a light-sensitive diazo resin or equivalent, to make our plates. On the other hand, magnesium silicate, copper silicate and aluminum silicate illustrate materials having such a high degree of insolubility as to be useless in the practice of our invention.

silicic acid, in solution, diluted with water to a concentration range of 1 percent to .1 percent Ludox, has been found to be a fully satisfactory equivalent of sodium silicate for our purposes, even though du Pont trade literature states that This product should not be considered as an alkali silicate, such as the sodium silicate of commerce, because in contrast to sodium silicate, it contains no significant quantity of alkali and in general Ludox as few properties in common with alkali silicates. However, the colloidal water dispersion of silica sold by Monsanto Chemical Co. under the trade name of Syton-W-ZO" and commonly known as a silica sol, disclosed by Jahoda in his U. S. Patent No. 2,433,515 for use in making photographic paper, not for making lithographic plates, has been found to be useless in the practice of our invention. From a comparison of those silicacontaiuing materials which are satisfactory in the practice of our invention and those which are unsatisfactory, it seems that at least one requirement for a satisfactory material is a concentration of the SiOz radical in solution at least equal to a certain minimum. Ludox furnishes enough SlOz radical to be effective for our purposes, whereas Syton-W-Zl) does not.

A preferred method of treating the aluminum foil or sheet material with the soluble silicate involves dipping a cleaned aluminum surface in the silicate solution maintained at temperatures of the order of 21'2 F. This can conveniently be done by running a web of aluminum foil continuously through an immersion bath. At these temperatures the soluble silicate will react with the surface of the aluminum to form an insoluble hydrophilic silicious surface. After this treatment, the excess soluble silicate, and any other soluble materials present, are immediately thoroughly washed away, and the treated foil or sheet is dried. The resulting silicate treatment on the surface of the aluminum foil or sheet is extremely thin but is very abrasion resistant. It is also substantially free of water-soluble material. It appears to be chemically bonded to the aluminum and apparently can only be abraded away by penetrating the surface of the aluminum sheet. The silicate treatment is very effective in rendering the surface of the aluminum permanently hydrophilic: the aluminum sheet in this form will not oxidize to a hydrophobic surface on exposure to air, as it will do in the absence of such a silicate treated surface or equivalent. Thus the silicate treatment or equivalent provides a permanently hydrophilic scum-preventing and tone-reducing film or treatment.

The silicate treated aluminum foil or sheet ust described is of quite a smooth character and usually has a metallic sheen or relatively smooth appearance,as contrasted Withthe dull appearance of various prior art grained plates. While some very slight amount of etching may unavoidably occur on the aluminum surface of the sheet during the cleaning operation, this is so small that it does not impart to the finished silicate treated sheet a rou h surface or a matte appearance. This is important in securing the highest performance characteristics, sought after in our finished presensitized lithographic plates, particularly where fine line work or fine half-tones are being reproduced.

The smooth silicate treated surface of our plate, for example produced as just described, without graining or deep etching, has the property of tenaciously holding image formed by exposure to light of light-sensitive organic nitrogen-containing material, e. g. light-sensitive diazo compounds, on the surface thereof, as described and illustrated hereinbelow.

Our silicate treated sheet is next treated with a solution of a light-sensitive diazo resin or equivalent. Suitable light-sensitive diazo resins are available commercially, from several manufacturers, e. g. Ringwood Chemi- I? cals, Inc. (formerly Edwal Laboratories, Inc.), Ringwood, Illinois.

One suitable method of making a suitable light-sensitive diazo resin is as follows: thirty-four parts of the sulfate salt of para-diazodiphenyl amine (available, for example, from the Fairmount Chemical Company, Newark, N. 1., at the present time as Para-diazodiphenyl amine salt) is mixed with 3.25 parts of para-formaldehyde and 4.5 parts of anhydrous zinc chloride. The above mixture is gradually introduced into 135 parts of cool sulfuric acid of 66 Baume, care being taken that the temperature does not exceed 6 C. When poured on twice its Weight of ice, the brown solution (obtained from the above reaction) decomposes to a black tarry material, essentially an impure diazo resin, which is removed and dissolvedin water. Addition of an excess of a saturated zinc chloride solution to this aqueous diazo resin solution precipitates a yellow solid which is removed; this yellow solid is then further purified by dissolving in water and precipitating by the addition of alcohol. This new precipitate is the purified light-sensitive diazo resin and, in the form of a dilute solution in water, for example, about a 1% solution, is used in applying a light-sensitive coating to our aluminum sheet or the like, above described, which has been given a silicate treatment or otherwise provided with a scum-preventing and tone-reducing film overlying and in contact with the surface of the metal, as herein illustrated.

The reactions and precipitations employed in the mak- I ing of the light-sensitive diazo resin are carried out under subdued light, for example, under a yellow light. This is also true of the operation of coating the silicate or like inorganic or other hydrophilic surface of the aluminum sheet with a dilute solution of the light-sensitive diazo resin or equivalent.

The dilute solution of light-sensitive diazo resin, just described, may be applied to the exposed surface of the permanently hydrophilic silicate treated sheet, or equivalent, above described, by a roll coating method, for example. Running the sheet in pressure contact with a rotating rubber roller, which is wet with the dilute diazo solution, applies a thin continuous coating of the diazo solution over the surface. It is preferred that the diazo coating be an extremely thin one, for example, leaving a residue of about 0.903 gram, or even less, e. g. 0.001 gram, of the diazo resin per square foot of plate area. For special purposes, e. g. to obtain a visible image after exposure, a heavier residue of diazo resin, but still a thin film, can be coated on the surface. When the diazo coating is dried, the treated and sensitized sheet is then die cut to standard plate sizes and, continuing under subdued light, the plates are packaged in light-tight packages, in which they are sent to the users and customers. The customer, in using the same, removes them from the package under subdued light and places a negative or sten cil thereover and exposes the same to ultraviolet light, to produce the desired image, as already described hereinabove.

Sensitized plates made according to our above described method are more sensitive to light than conventional albumin, ammonium bichromate plates; and our plates can be sufficiently exposed in about two-thirds the time.

Scratches, fingerprints and other foreign matter will impair the light-sensitive surface, and the plate, there fore, should be handled carefully, by the edges. After the plate has been exposed, if it is going to be stored for a period of time, a desirable precaution is to coat the image with a gum arabic solution, which gives mechanical protection to the image and then can easily be washed off with water when it is desired again to use the plate.

Conventional grained zinc plates (whether they have the usual albumin, ammonium bichromate light-sensitive coatings, or are otherwise sensitized according to the prior practice) are so subject to attack by the oxygen of the air that it is necessary for the lithographer to coat the image surface of such a plate with a gum arabic solution, to protect it, even while he goes to lunch, whereas our plates are resistant to oxidation, due to our scum-preventing film, e. g. of silicate or the like, and such protection by a gum arabic solution is not needed even though a plate would remain inactive on a lithographic press for a considerable time.

Exposure of our presensitized lithographic plates may be carried out in a printing frame under a source of ultraviolet light. Carbon arcs may be used but are not required. Photo-flood bulbs and black light fluorescent tubes will also give satisfactory results. While the exposure time is not critical, under-exposure may result in broken images or no image at all. Extreme over-exposure may cause dirty highlights and blocked-up shadows in half-tone areas. While the user of our presensitized plates has considerable latitude in the amount of exposure, the foregoing will serve to guide him from undue extremes of over-exposure or under-exposure.

Suggested exposure times for the following light sources are:

Minutes Bank of 15 watt BL light tubes at 6" 2-4 35 amp. carbon are at 24" 1-2 After exposure the plate (where a diazo resin is used as the sensitizer) is desensitized by wiping with a solution of gum arabic, which dissolves and removes the unreacted diazo sensitizer. At this point the image is invisible. While the plate is still Wet with the gum arabic solution, an image developer or strengthener consisting of a resin emulsion (or, alternatively, a printers developing ink of conventional type) is poured on the plate and rubbed in quickly with a soft pad or cotton wad. The excess image developer should be wiped away before it dries completely. The resinous portion of the image developer should preferably contain a pigment or dye which will make the image clearly visible as the particles of resin adhere to the hydrophobic and organophilic image. The plate is then ready for the press, or it may be coated with gum arabic if it is to be stored before use.

Our lithographic plates require the use of less water on a lithographic press than is required where the conventional prior art grained zinc plates are used. This is a factor in giving more brilliant colors in lithographic reproductions made from our plates, since the reduction of color brilliancy caused by emulsification of water and ink in the case of grained Zinc plates is greatly minimized where our plates are used.

Where our plates are used, less ink is also required to give the same tone values in the finished work, and especially so in multicolored printing, thereby significantly reducing the drying time required between the printing of successive colors.

After our plate (made, for example, with a diazo lightscnsitive resin) has been installed on a lithographic press. the gum arabic coating (if previously applied) is removed by sponging with water or with a weak fountain solution. The fountain rollers should be dropped first and, after a few revolutions, the ink rollers may be dropped. The image should ink up quickly. No special inks or fountain solutions are required, and most materials commonly used for this purpose will be found to be satisfactory for use with our plates. in order to obtain the maximum number of satisfactory impressions, the press should be carefully adjusted to the least pressure consistent with quality printing.

Our lithographic plates are of such nature, due to the particular materials and the thickness thereof, that they do not wrinkle or stretch during processing or on the press (as do paper or plastic planographic plates, for example) and, therefore, are particularly suitable for 1 9 lithographic printing, even where very accurate registration is required.

One advantageous type of aluminum foil to be used for our process, in the manner above described, is one produced by the Aluminum Company of America and designated as 381-119, the same containing about 1.25% manganese alloyed with the aluminum. There are some other types of aluminum foil or sheeting which would be too soft and pliable to be well suited for our use if employed in the form of relatively thin gauge sheets, although any commercial type of aluminum which is stifl enough to resist wrinkling and creasing, in the form of thin sheets or foil, may be employed.

While aluminum appears, at the present time, to be our preferred metal backing sheet material, on the basis of cost, handling properties and such like, we have also successfully employed sheets of lithographic zinc, foils of copper, lead and tin, electro-deposited chromium and copper surfaces, sheets of commercially pure magnesium,'

polished sheets of tantalum and a sheet of titanium known as Ti-75A, treating the same with a silicate or the like, as above illustrated, to render the metal surface permanently hydrophilic and to provide a scum-preventing film or surface to which an insoluble diazo image will strongly adhere. Still other metals may be employed in making our presensitized planographic plates, so long as a strongly adherent or chemically bonded silicate or other permanently hydrophlic coating or treatment can be applied thereto, with suitable control of conditions, but we believe that the amphoteric metals, as a class, provide the best surfaces on which to apply silicate or equivalent permanently hydrophilic surface treatments.

While water-soluble or water-dispersible silicates of commerce are the most desirable and convenient materials for producing permanently hydrophilic surface treatments on metal sheets for our purposes, yet with variations in metal sheets and/or with variations in the light-sensitive organic material to be employed and/or with variations in the treating procedure, treating materials other than the water-soluble silicates may be useful or even preferred.

For example, other silicon-containing compounds such as Ludox colloidal silica or saturated solutions of calcium silicate have been employed by us, experimentally, as treating materials, because of special characteristics of these solutions, such as stability, lower alkalinity and others. Certain non-silicon compounds, e. g. certain polyhydroxy and polymolecular organic acids have also been experimented with, which render metal surfaces permanently hydrophilic and of a scum-preventing nature, and provide a strong bond between the metal surfaces above described and light-reacted diazo resin or the like. Further information on this matter will be made the subject of a separate application.

Where solutions of calcium silicate or silicic acid are used, for example, in place of sodium silicate, treating temperatures of the order of ISO-212 F. can be used, and the conditions of treatment may otherwise be similar to those described above for sodium silicate.

Diazo materials, especially diazo resins, have been described herein as the preferred light-sensitive materials for our purposes. However, variations in this regard are contemplated.

it has been found, for instance, that the azide of our preferred diazo resin can, with suitable modifications, be used as the light-sensitive coating. This polymeric azido resin is not water soluble and only slightly soluble in common organic solvents, but a concentration suitable for coating can be obtained using as solvents toluene or methyl cellosolve, or mixtures of these, or other organic solvents. After exposure through a negative or stencil the un-light-decomposed azide can conveniently be re moved by a water-toluene mixture, leaving a hydrophobic printing image of water-insoluble, light-reacted azide.

It is possible to prepare and use, as light-sensitive materials, other polymeric azido resins, particularly aromatic azido resins, which seem to be particularly useful, and also aliphatic azido resins. Similarly, diazo oxides (see The Aromatic Diazo Compounds, by K. H. Saunders, published 1949 by Edward Arnold & Co., London, page 29 thereof), both monoand poly-molecular have been found to be useful light-sensitive compounds in making our plate. The mono-molecular imino-quinone-diazide (see page 24 of said book by Saunders) made from the monomer of our preferred diazo resin has also been found to be useful. Certain parwtertiary-amino-diazo resins can be prepared and are useful. The preparation of polyvinyl cinnamate light-sensitive materials has been recently disclosed and at least certain of these materials have been found to be useful in the practice of this invention.

While we have just pointed out variations and modifications of our invention, the form of our planographic plate which has been marketed by the assignee of this application since a few months prior to the filing of our aforesaid parent application Serial No. 199,566 is made with an aluminum sheet, having a permanently hydrophilic silicate or silicon-containing scum-preventing film or surface treatment bonded thereto, and a thin lightsensitive diazo resin coating over the hydrophilic silicious surface.

Hereinabove we have made reference to various illustrative descriptions of lithographic plates in the prior art. We are also aware that it has been known or suggested heretofore that aluminum be treated or coated with sodium silicate, for one purpose or another. For example, see: Soluble Silicates in Industry by James G. Vail, published in the year 1928, by the Chemical Catalogue Co., Inc, New York, N. Y., at page 371 thereof; The Aluminum Industry, by Edwards et al., published in 1930, by McGraw-Hill Book Company, Inc., New York, N. Y., page 771 thereof, for example; Simons, U. S. Patent No. 2,132,443, granted October 11, 1938; Champion et al., U. S. Patent No. 2,225,736, granted December 24, 1940; Ayers, U. S. Patent No. 2,233,573, granted March 4, 1941; Toland et al., U. S. Patent No. 2,311,889, granted February 23, 1943; and Mason, U. S. Patent No. 2,507,314, granted May 9, 1950. However, none of the patents or other disclosures just identified, nor any others to our knowledge, disclose or teach our improved presensitized lithographic plate or any plate of similar utility or like advantages. Vail describes the action of sodium silicate on aluminum as a detergent in cleaning aluminum. Edwards et al. describe a use of sodium silicate as a corrosion inhibitor. Simons describes a paper lithographic plate in which silica, freshly precipitated from sodium silicate, is used to form, a grained printing surface. Champion et al. describe a direct image printing plate in which the margins only are coated with sodium silicate to provide a smudgeproof border. Ayers employs sodium silicate, said to serve as a protective coating, over the printing face of an exposed albuminbichrornate coated zinc plate. Toland et a1. provide a rough, grained surface on paper-backed lithographic plates by applying to the paper a mixture of clay, calcium carbonate or silica, bonded together with sodium silicate, as a base for an albumin typelightsensitive coating. Mason provides a method for the multiple etching of aluminum to produce matte surfaces, and may employ sodium fluoride and sodium silicate in his operation. However, none of these patents or publications disclose a presensitized plate of any type.

It will be understood, however, that our invention concerns, not merely a presensitized plate, but a presensitized plate in which a metal surface, preferably a smooth metal surface, e. g. aluminum, is provided with a permanently hydrophilic thin film or surface treatment, preferably formed from an aqueous sodium silicate solution or equivalent and chemically bonded to the metal surface; and having applied to the silicate, or other permanently hydrophilic surface or scum-preventing and tone-reducing film, a thin coating of a light-sensitive diazo resin, or other light-sensitive organic material which, upon exposure to light, will tightly and preferably chemically bond itself to the silicate or other permanently hydrophilic surface. Our presensitized planographic plate, of the construction just summarized, and hereinabove illustrated, provides a new article for commerce and industry. It is a plate which will yield high quality reproductions and long plate life, as well as fulfilling other objectives above set forth.

While we have described our novel article primarily in connection with its use as a lithographic plate, it has other uses. For example, our plates can be used to advantage in the photographic preparation of permanent metal name plates, instruction panels, templates, Wiring diagrams, dial and scale faces, advertising specialties, signs, maps and the like. For these purposes, the plate is exposed to ultra-violet light through a photographic negative, followed by desensitizing and inking or de veloping as described above. The visible image may be produced by the use of an ordinary lithographic printing ink'or an image developer, such, for example, as that disclosed above and also described in detail in the co pending application of Myron Hall, Serial No. 239,841. After the developed plate with its visible image has been washed and dried, it may be used as such, or the surface may be further protected by spraying with a clear lacquer. Such plates may be fastened to machinery and the like, and made a permanent part thereof, to aid in the operation and maintenance of the machinery, and to identify its parts, its manufacturer, etc. This use of our invention is becoming of increased importance.

Hereinabove We have referred to scumming, scumpreventing and such like. In Photography and Plate Making for Photo-Lithography, by I. H. Sayre, published in 1949 by Lithographic Textbook Publishing Company, Chicago, at page 435, in the Glossary, the following definition is given: Scumming-the press plate takes ink in the non-printing areas and transfers it to the paper. Also see Plate Iroubies in Offset Lithography, Shop Manual No. 31, issued in 1947 by Lithographic Technical Foundation, Inc., New York, at page 10 thereof. Also note use of the terms scum-preventing and tone-reducing in Australian Patent No. 155,324.

Insofar as we are aware, prior to our invention there had never been a satisfactory presensitized metal lithograph plate; nor had there been any presensitized metal lithographic plate on the market.

Hereinabove we have attempted to describe and illustrate our invention in various details, and not to limit it. All modifications and variations which are within the scope of the appended claims are contemplated.

What we claim is: j

l. A presensitized, dimensionally stable plate suitable for lithographic printing and related uses, and capable of being shipped in light-proof packages, stored and then used weeks or months after manufacture, com prising an aluminum sheet having on at least one surface thereof a permanently hydrophilic scum-preventing and tone-reducing film formed by reacting an aqueous solution of a soluble silicate with the surface of said aluminum sheet, said film overlying and being firmly bonded to said surface of said sheet and being substantially free of water-soluble material, said film being fur ther characterized in that it willcause an in situ insolubilized diazo image strongly to adhere to the surface of the sheet, and overand in contact with said film a thin coating of a light-sensitive diazo resin, said lightsensitive material being characterized in that, upon exposure of the plate to ultra-violet light through a stencil or negative, it will react in the exposed portions, expelling nitrogen from the molecule and forming a water-insoluble hydrophobic and organophilic material which is tightly bonded to said permanently hydrophilic thin metal sheet from the class consisting of aluminum,

zinc, tin, magnesium, chromium and copper, said metal sheet having on at least one surface thereof a permanently hydrophilic scum-preventing and tone-reducing film formed by reacting an aqueous solution of a soluble silicate with the surface of said metal sheet, said film overlying and being firmly bonded to said surface of said sheet and being substantially free of water-soluble material, said film being further characterized in that it will cause an in situ insolubilized diazo image strongly to adhere to the surface of the sheet, and over and in contact with said film a thin coating of a light-sensitive diazo resin, said light-sensitive material being characterized in that, upon exposure of the plate to ultra-violet light through a stencil or negative, it will react in the exposed portions, expelling nitrogen from the molecule and forming a water-insoluble hydrophobic and organophilic material which is tightly bonded to said permanently hydrophilic film, providing a printing image, the light-sensitive resin material being readily washed away from the unexposed areas, leaving the permanently hydrophilic film bare in said areas, said hydrophilic film eing further characterized in that it will prevent the metal from causing decomposition of the diazo lightsensitive material, thus providing long shelf life for the presensitized plate.

3. A presensitized planographic plate comprising an aluminum sheet having at least one smooth surface thereof rendered permanently hydrophilic by treatment with an aqueous solution of an alkali metal silicate, said permanently hydrophilic surface being provided by a thin layer of the reaction product of said aluminum and said silicate and being substantially free of water-soluble materials, said permanently hydrophilic surface being coated with a thin coating of a water-soluble light-sensitive diazo resin, said diazo resin being characterized in that, upon exposure of the plate to ultra-violet light through a stencil or negative, it will react in the exposed portions to form an image of water-insoluble, hydrophobic and organophilic material which is tightly bonded to said permanently hydrophilic surface, the diazo resin remaining water-soluble and capable of being readily washed away clean from the unexposed areas, leaving said permanently hydrophilic surface bare in said areas.

4. A plate suitable for use in planographic printing and related uses comprising an aluminum sheet having on at least one surface thereof an extremely thin layer of the reaction product of said aluminum sheet and an aqueous solution of an alkali metal silicate, providing a permanently hydrophilic surface, said surface being substantially free of water-soluble materials, and said surface having thereover a thin coating of a water-soluble light-sensitive diazo resin, which, upon exposure of the plate to ultra-violet light through a stencil or negative, will react in the exposed portions to form an image of water-insoluble, hydrophobic and organophilic material which is tightly bonded to said permanently hydrophilic surface.

5. A plate suitable for use in planographic printing and related uses comprising a sheet having as at least one surface thereof a metal from the class consisting of aluminum, zinc and tin, and over and bonded to the surface of said metal an extremely thin layer of the reaction product of said metal and an aqueous solution or 13 an alkali metal silicate, providing a permanently hydrophilic surface thereon, said surface being substantially free of water-soluble materials, and said surface having coated thereover a thin coating of a Water-soluble lightsensitive diazo resin.

References Cited in the file of this patent UNITED STATES PATENTS 208,114 Obernetter Sept. 17, 1878 711,101 Foerster Oct. 14, 1902 1,325,890 Freuder Dec. 23, 1919 1,574,378 Dobinson Feb. 23, 1926 2,433,515 Jahoda Dec. 30, 1947 2,507,314 Mason May 9, 1950 FOREIGN PATENTS 6,857 Great Britain of 1914 14,344 Great Britain July 11, 1921 322,007 Great Britain Nov. 28, 1929 402,737 Great Britain Mar. 4, 1932 407,830 Great Britain Mar. 29, 1934 14 Great Britain Aug. 7, 1935 Great Britain Aug. 12, 1935 France May 5, 1899 France Dec. 23, 1940 France July 12, 1943 France Feb. 19, 1945 Germany Oct. 23, 1924 Germany Sept. 15, 1928 Germany Aug. 31, 1932 OTHER REFERENCES Hi-Speed Processing Plate, publication in The National Lithographer, May 1949; 2 pages; page 40 and page 60; page 40 particularly relied upon.

5 Ilford Manual of Process Work, L. P. Clerc, fourth edition, 1946; Ilford Limited, Ilford, London, pages La Technique des Reproductions Photomechaniques, L. P. Clerc, vol. 1, 1947, Etablissements Bouzard-Cal- 20 mels, Paris, pages 356, 357 and 509-519 

1. A PRESENSITIZED, DIMENSIONALLY STABLE PLATE SUITABLE FOR LITHOGRAPHIC PRINTING AND RELATED USE, AND CAPABLE OF BEING SHIPPED IN LIGHT-PROOF PACKAGES, STORED AND THEN USED WEEKS OR MONTHS AFTER MANUFACTURE, COMPRISING AN ALUMINUM SHEET HAVING ON AT LEAST ONE SURFACE THEREOF A PERMANENTLY HYROPHILIC SCUM-PREVENTING AND TONE-REDUCING FILM FORMED BY REACTING AN AQUEOUS SOLUTION OF A SOLUBLE SILICATE WITH THE SURFACE OF SAID ALUMINUM SHEET, SAID FILM OVERLYING AND BEING FIRMLY BONDED TO SAID SURFACE OF SAID SHEET AND BEING SUBSTANTIALLY FREE OF WATER-SOLUBLE MATERIAL, SAID FILM BEING FURTHER CHARACTERIZED IN THAT IT WILL CAUSE AN IN SITU INSOLUBILIZED DIAZO IMAGE STRONGLY TO ADHERE TO THE SURFACE OF THE SHEET, AND OVER AND IN CONTACT WITH SAID FILM A THIN COATING OF A LIGHT-SENSITIVE DIAZO RESIN, SAID LIGHTSENSITIVE MATERIAL BEING CHARACTERIZED IN THAT, UPON EXPOSURE OF THE PLATE TO ULTRA-VIOLET LIGHT THROUGH A STENCIL OR NEGATIVE, IT WILL REACT IN THE EXPOSURE PORTIONS EXPELLING NITROGEN FROM THE MOLECULE AND FORMING A WATER-INSOLUBLE HYDROPHOBIC AND ORGANOPHILIC MATERIAL WHICH IS TIGHTLY BONDED TO SAID PERMANENTLY HYDROPHILIC FILM, PROVIDING A PRINTING IMAGE, THE LIGHT-SENSITIVE RESIN MATERIAL BEING READILY WASHED AWAY FROM THE UNEXPOSED AREAS, LEAVING THE PERMANENTLY HYDRROPHILIC FILM BARE IN SAID AREAS, SAID HYDROPHILIC FILM BEING FURTHER CHARACTERIZED IN THAT IT WILL PREVENT THE METAL FROM CAUSING DECOMPOSITION OF THE DIAZO LIGHT-SENSITIVE MATERIAL, THUS PROVIDING LONG SHELF LIFE FOR THE PRESENSITIZED PLATE. 